The present invention relates generally to optical disk storage systems and, more particularly, to an optical disk storage system in which the optical transducer is mounted in a slider in contact with the storage medium at an operating speed which utilizes the tribo-attractive effect to minimize wear.
In magnetic storage systems, an information bit is stored by focusing a magnetic field to a small volume on the disk to align the magnetic domains in that volume to a desired orientation. In optical storage systems, an information bit is stored by focusing a laser beam onto a small spot on the optical disk to heat the medium and thus effect a physical change in the medium material at that spot. In the case of magneto-optic storage systems, the heat generated by the laser beam causes the magnetic domains at the spot location to be aligned with an applied magnetic field. In all moving disk storage systems, the demand for increased storage capacity is presently being met by increasing the areal bit density on the storage disk.
In magnetic disk storage systems, increase of areal bit density requires the reduction of three basic parameters, the magnetic write transducer (head) gap length, the thickness of the magnetic storage media and tile head to disk separation. Given a specified gap length and media thickness, the smaller the head-disk separation, i.e., tile lower the head flying height, is, the smaller the bit cell size which can be achieved is. The limit of lower flying height is contact recording, in which the slider is in physical contact with the rotating magnetic disk, i.e., the slider is sliding or rubbing continuously on the disk surface and the read/write transducer is as close as the edge of the slider can be to the disk surface. U.S. Pat. No. 4,819,091 to Brezoczky et al, assigned to the instant assignee, discloses a magnetic contact recording system comprising a magnetic read/write head mounted on a slider which is in physical contact with the rotating storage medium. A tribo-attractive force is generated between the moving disk surface and the slider which counteracts the lifting force generated by the moving air layer adjacent the disk surface and which allows contact recording and reading of data without excessive wear to either the magnetic head and slider or the recording medium.
In an optical storage system, a laser beam is projected onto the optical storage medium (optical disk) and focused to a small spot on the disk surface through an optical transducer or head. In prior art optical systems, the optical head is maintained well above the medium surface and the beam spot size is defined by the laser light wavelength (.lambda.) and conventional optics. It has been generally believed that the diffraction limit in air of about .lambda./1.5 is the fundamental lower bound in resolution for any optical image recording. Thus, the primary means of increasing areal bit density in an optical or magneto-optical system has traditionally been to utilize laser beams of shorter wavelength. The beam output of injection lasers presently in use have wavelengths on the order of 1 micrometer (.mu.m). New lasers, use of second or higher order harmonics and frequency multipliers are currently being explored. However, considerable difficulty is being encountered and the likelihood of development of new lasers having suitable characteristics in the near future is low. On the other hand, there has been steady improvement in the reliability and power capabilities of the currently used conventional semiconductor lasers which is likely to continue due to their wide use.
To achieve high density optical recording at or near the diffraction limit utilizing conventional semiconductor lasers it is necessary to very tightly focus the laser beam. This requires high numerical aperture objective lens which means that the lens must be maintained very precisely at the focal distance from the optical medium. Typically, focus is accomplished by an electro-mechanical servo system which maintains the optical head at the required distance from the medium thus adding to the mass and size of the optical head. Alternatively, in systems which do not physically adjust the distance of the head from the medium, relatively complex focusing systems elsewhere in the system are required to compensate for the varying head height.